WinISD resonance frequency for sealed enclosure

[audio_04]

Hi everyone,

I'm currently working on a 2-way DIY speaker project using the Dayton Audio DSA135-8 as the woofer in a sealed enclosure. I measured the driver's T/S parameters myself, and I'm noticing a slight discrepancy between my manual calculations and what WinISD is outputting for the system resonance frequency (fc).

Here are the parameters I measured for the woofer:

• fs=59 Hz
• Vas=7.3 L

I am planning a sealed box with an internal volume of 8 liters (Vb=8 L).

If I calculate the theoretical system resonance using the classic formula:

fc=fs*root(1+Vas/Vb)
Plugging in my numbers, I get:

fc=59*root(1+7,3/8) =81,593
However, when I input these exact same parameters into WinISD and set the box volume to 8 L, the software simulates a system resonance of 85 Hz.

I know it's only a small difference of about 3.4 Hz, but I'd like to understand the math behind it.

 

[ernperkins]

For a sealed box there are two parameters, Ql (box losses due to cabinet leaks) and Qa (box losses due to cabinet absorption) that can affect box tuning parameters. To see these in WinISD select "Box" and click on "Advanced". Here's a description from the late Jeff Bagby:

Ql is the Q at Fb due to box losses from leakage. As Ql approaches infinity losses will approach 0. A system with no leakage will have a Ql of 50. Very small leaks will have a value of 30, small minor leaks will be about 20, and significant leaks will have values of 5-10. Normal values will range from 40 to 10, with 20-30 being a fairly typical system. Values in the range of 10 will represent many porouse cabinet and cones, 5 will represent leakage like you would see when using an Aperiodic vent. Use these numbers as a guideline for adjusting these values.

Qa is the Q at due to box losses from absorption. As Qa approaches infinity losses will approach 0. High values >100 will represent very low losses. Normal values will range from 120 to about 5. As a guideline, an enclosure with no fll at all would have a Qa value of 120, a small amount of dacron in the box would bring it to about 100-80, walls covered with foam would be about 40, covered with thick fiberglass or a heavy damping pad would bring it to about 20. A fully stuffed box would be 5-10 depending on stuffing density.